Water lettuce isn't a fancy green for salads; it is manatee food, capable of smothering a river and the focus of growing controversy.

Water lettuce is regarded officially as a destructive exotic from another country and appropriate for blasting on sight with chemical weaponry. Some think, however, the plant is a native Floridian that has a valued role in the environment.

"I'm not sure where we need to go to get it off the hit list," Lake County environmental activist Linda Bystrak said.

The place of water lettuce has been debated quietly for years. Nobody disputes its ability to grow like a weed and to clog a waterway. It thrives in waters — this is a Florida specialty — polluted by nutrients from sewage and fertilizers.

Last year, state and federal agents sprayed 46,000 acres of water lettuce and other commingling weeds in Florida at a cost of $5.8 million.

The stuff is still almost everywhere in the state, and anybody who has boated has probably seen it.

"I'm a kayaker," Bystrak said. "I've paddled through it."

Advocates for water lettuce say if reclassified as a native, it may be given greater respect for its ability to remove pollution from rivers and lakes and serve as food and habitat for wildlife.

Jessica Spencer, a biologist with the U.S. Army Corps of Engineers in Jacksonville, said whether the plant is native or exotic is not the main concern.

It can outgrow most everything else, shade out desired plants that grow on riverbeds and make boating impossible, she said.

Spencer said her agency is aware that manatees eat water lettuce, but that's partly because the plant may have choked out other food.

"It's a balancing act," she said of her agency's congressional assignment to control the aggressive plant with herbicide. "We take a lot of calls from people angry about us spraying water lettuce or from people who want us to spray."

The state Fish and Wildlife Conservation Commission says this about water lettuce on its website: "This floating plant native to South America is considered to be one of the worst weeds in the subtropical and tropical regions of the world."

The Florida Exotic Pest Council classifies water lettuce as a "category 1" exotic that wrecks the state's environments. The label is a potent justification for spending millions to kill it.

And that should be rethought, said Jason Evans, an environmental-sustainability analyst at the University of Georgia's Carl Vinson Institute of Government.

An Orlando native, Evans has spent years gathering evidence that water lettuce was present in Florida many thousands of years ago.

Fossil, seed and pollen findings by other researchers make it clear the plant is a native Floridian, Evans said, while evidence that Spanish adventurers brought it to Florida is weak.

"The only question left is whether varieties from other parts of the world were introduced in Florida," Evans said.

Strongly disagreeing is Colette Jacono, botanist at the Florida Museum of Natural History. She said there needs to be rigorous science done to finally determine the plant's origin. She is working with U.S. Department of Agriculture scientists to evaluate the fossil evidence cited by Evans and to trace the genetics of plants found in Florida.

"Water lettuce is an interesting and attractive native plant in Florida's waters, and it should be allowed to coexist with our other native flora," said Bob Knight, a wetlands-and-springs scientist.